Magnet-core.



G. W. ELMEN.

MAGNET CORE.

APPLICATION FILED APR. 2. 1918.

1,297,126. Patentd Mar. 11,- 1919.

fly 6 A 4/13.

UNITED STATES PATENT OFFICE.

GUSTAF W. ELMEN, OF BOGOTA, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MAGNET-CORE.

Specification of Letters Patent. Patentea Mar, 11 1919.

Application filed April 2, 1918. Serial No. 226,283.

To all whom it may concern:

Be it .known that I, GUSTAF W. EL uraN, a citizen of the United States, residing at Bogota, in the county of Bergen, State of New Jersey, have invented certam new and useful Improvements in Magnet- Cores, of

which the following is a full. clear, concise,

and exact descriptlon.

This invention relates to magnet cores generally and particularly to cores for loading coils for telephone circuits. Its general object is to provide a new and improved core material which is cheap to manufacture, which is easily formed into the deslred shape, and which possesses to a hlgh degree those characteristics most advantageous in cores for loading coils and other electrical apparatus. I

The present invention may be considered an improvement upon the magnet cores described and claimed in application for Letters Patent, Serial No. 89,409, filed April 6, 1916, in the name of James Buckner Speed, for improvement in magnet cores; Serial No. 89,467, filed April 6, 1916, in the name of the present applicant, for improvement in magnet cores; and Serial No. 100,056, filed May 26, 1916, in the name of John C. Woodrufi, for improvement in magnet cores; all of which applications are assigned to the same assignee as the present application.

The above identified applications, generally speaking, describe magnet cores and partlcularly loading coil cores composed of finely divided magnetic material and insulating material separating the particles of the magnetic material, said compound being compressed into a self-sustaining solid body by subjecting the mass to pressure suflicient to 've it a specific gravity approximately t e same as the specific gravity of the undivided magnetic material, and probably s'iflicient to distort some at least of the magnetic particles beyond their elastic limits. In the Speed application above mentioned, iron-by-hydrogen is referred to as i the most suitable magnetic material; and in the ap lications of Elmen and. Woodruif, finely divided and annealed electrolytic iron is mentioned as the preferred magnetic material. It is a fact, however, that either iron-by-hydrogen or annealed electrolytic iron is more expensive to produce than unannealed electrolytic iron. Furthermore,-

ent invention, therefore, relates to a ma use in cores in telephone circuits with which are combined telegraph circuits, reduces the disturbances in the former, due to the transmission of telegraph messages.

The present invention makes the use of unannealed electrolytic iron possible and is the result of the discovery that if hard particles of magnetic material such, for example, as the unannealed electrolytic iron above refered to, are mixed with softer particles, such as annealed electrolytic iron or iron-by-hydrogen, magnet cores may be obtained which, while having sufiicient mechanical strength, also possess approximately the same magnetic characteristics as cores formed only of hard particles. Furthermore. by varying the proportions, of soft and hard particles, cores to meet difi'erent requirements may be produced. The preset core characterized by the fact that parti c les of magnetic materials of different degrees of hardness and therefore of difierent magnetic characteristics, are intermixed and subjected to compression to form a hard self-sustaining body of selected magnetic characteristics.

In the drawing, Figure 1 is a perspective view of a section of a loading coil core made in accordance with the present invention; and Fig. 2 shows a plurality of these sections assembled to form a complete core. It will be understood, however, that this is merely illustrative, and that the invention is not limited to the production of this form of core, but is adapted to the making of cores of many forms.

Magnetic material for magnet cores em-. bodying the. present invention may be obtained by reducing electrolytic" iron obtained in any well-known manner, (for example, from a cell containing a bath of ferrous ammonium sulfate), to a finely divided state, as by grinding in a ball mill. Experience has shown that for the best results the particles used in core making should not be arger in size than what will pass through an 80-mesh screen.

The fine particles into which the brittle o though some of electrolytic iron is broken by the grinding operation are, for small magnetizing forces, of low magnetic retentivity and therefore would make a core having an extremely low hysteretic characteristic under the influence of ordinary telephonic currents. But on account of their mechanical hardness, a mass of such particles is not readily molded into a solid core.

Therefore, in accordance with the present invention, there is mixed with the finely divided product of the grinding operation five to ten per cent. or more of finely divided soft iron, such as either of the forms above referred to, i. 6., iron-by-hydrogen or annealed ground electrolytic iron. The latter material is readily obtained by heating ground electrolytic iron, procured as above described, in a suitable form of furnace to a sufiicient extent to anneal it to the desired degree.

The hard and soft particles are.thoroughly intermixed so that the soft particles are distributed evenly throughout the mass of harder particles. Either before or after the intermixing, both kinds of particles are individually insulated. This may be accomplished by producing on each particle a surface coating of red iron oxid, as by adding to a mass of the pure iron particles approximately ten per cent. by weight of water and then heating and stirring the mixture in the presence of air until dried. A preferred method is that set forth in Woodruff application, Serial No. 100,056, above referred to, and consists in giving each of the, particles a zinc coating by tumbling them in a drum with pieces of zinc for several hours. To themass of zinc-coated particles is added a thin solution of insulating material such as shellac and the mixture stirred until the zinc-coated iron particles are thoroughly covered with shellac, after which the alcohol of the shellac solution is evaporated from the mixture "by slowly tumbling the mass in a tumbling barrel through which a current of air is drawn.

The mixture of zinc and shellac-coated hard and soft iron particles is subjected, in suitable molds, to pressures of approximately 200,000 to 250,000 pounds per square inch. This probably results in distorting the softer particles beyond their elastic limits, so that by reason of the permanent set which they are thus given they interlock ith the harder particlesand bind the mass into a hard self-sustaining solid body, havng/a spec fic gravity of 6.5 or higher, that 1s, 'approx1mately 7,-.which isabout that of the; undivided iron. The harder particles are probably little changed inshape, al-

them may suffer fracture rwithout, however, being disintegrated; but

neither this nor puncturing of the insulating coats of the particles occurs to a'sufiicient extent to materially decrease the electrical resistance of the mass.

In practice, it has been found desirable in making loading coil cores to use core sections having a thickness of about one-fifth of an inch and to use five or more sections in building up a core, a suitable insulating material such as paper, lacquer or shellac, being interposed between the sections. Fig. 1 shows in perspective such a core section or ring 3; and Fig. 2 shows the built-up core. As shown, the outside edges of the outside 4 core sections 4: and 5 are rounded, this being in order that the windings may closely conform to the surface of the core.

It has been found that a core made in the manner above described is strong mechanically and stable chemically. It has as high specific resistance as one containing only soft iron particles, its hysteretic characteristic is considerably lower, and its magnetic stability is greater.

Although as set forth in the preceding paragraphs, it is preferable to add to the unannealed product of the grinding mill at least five per cent. of specially prepared soft iron particles, it has been found that by using suflicient pressure solid magnet cores may be madeof insulated particles of unannealed electrolytic iron only; and it is thought that the binding efl'ect in such cores is possibly dueto the fact that some of the particles received from the grinding mill, without being annealed, are capable of undergoing a permanent distortion when sufiicient pressure is used, say 250,000 pounds to the square inch. Thus it is practicable, in accordance with this invention, to construct magnet cores of finely divided magnetic material such as iron in which hard particles and soft particles are present in any desired proportion; and therefore since the hard and soft particles differ both magnetically and mechanically, cores may readily be produced whose mechanical and electromagnetic characteristics vary between the extremes exhibited by cores in which practically all the particles are relawill-therefore be seen that this invention provides a simple and highly eflective means of meeting various practical require-2 ments as to the mechanical and electromagnetic characteristics of magnet cores, and particularly. of loading coil cores.

What is claimed is: 1. A magnet core composed of finely divided and intermixed magnetic materials differing substantially in their magnetic characteristics, and insulating material separating the particles of magnetic material.

2. A magnet core comprising finely divided and intermixed magnetic materials of substantiallydifferent degrees of hardness, and insulating material separating the particles of magnetic material.

3. A magnet core composed of insulated particles of unannealed electrolytic iron and insulated particles of annealed electrolytic iron intermixed and united into a solid body.

4. A magnet core comprising finely divided intermixed magnetic materials of different degrees of hardness and insulating material separating the particles of magnetic material, the mixture being compressed to an extent sufiicient to permanently distort the softer particles of magnetic material.

5. A magnet core composed of finely divided and intermixed magnetic materials of diflerent degrees of hardness and insulating material separating particles of magnetic material, the mixture being compressed to an extent suflicient to permanently distort the softer particles of magnetic material without appreciably affecting the harder particles.

6. A magnet core composed of finely divided and intermixed magnetic materials differing in their magnetic characteristics, and insulating material separating the particles of magnetic material, said compound having a specific gravity of approximately 7.

7. A magnet core composed of finely divided and intermixed magnetic materials of different degrees of hardness, and insulating material separating the particles of magnetic material, said compound having a specific gravity of approximately 7.

8. A magnet core composed of insulated particles of unannealed electrolytic iron and insulated particles of annealedelectrolytic iron intermixed and united into a solid body having a specific gravity of approximately'7.

Inwitness whereof, I hereunto subscribe my name this 27th day of March, A. 1)., 1918.

GUSTAF W. ELMLEN. 

